1. Field of the Invention
The present invention relates to a dry type wire drawing process for continuously drawing a wire rod or a steel bar (which will be conveniently referred to as a "wire").
2. Description of the Prior Art
In a general example of a secondary working operation for a wire to be cold-forged into bolts or nuts, the wire is pickled so that it may be descaled. Next, the descaled wire is treated with a lubricant and is then subjected to a primary drawing operation. After that, the drawn wire is annealed to spheroidize the cementite so as to give a high cold-forgeability. The wire once drawn is pickled and treated with a lubricant at a second stage and is then secondarily drawn by the so-called "skin pass".
In the prior art, the pickling treatment, the surfacing treatment for lubrication, and the lubricating treatment are conducted by the batch-type process, by which a coiled wire is hung by means of a C-shaped hook so that it may be consecutively immersed in and transferred to and from the respective treating liquid baths. As a result, the batch-type process suffers from problems: that the productivity is so low as to raise the cost; that an additional cost for disposing the respective treating liquids is high because the environmental pollution has to be considered; that satisfactory working circumstances are not always provided because the treatments are of the wet type; and that inspection of the product over the whole length is difficult.
Here, liquid zinc phosphate is used as lubrication surfacer of the prior art, and a liquid which is prepared by dissolving either powdered metallic soap or a mixture of lime and metallic soap is used as the lubricant. However, the cost for this process is high. Moreover, the wire to be cold-forged is subjected to the surfacing treatment with a lubricant, i.e., zinc phosphate having an excellent lubricity although this lubricant is expensive, because the lubricant used for the drawing treatment effects, as it is, the lubrication required for the cold-forging treatment.
For the more and more severe requirement for qualities in recent years, on the other hand, flaw detection and repair of the drawn wire become more and more important treatments. Generally speaking, however, the in-line flaw detection and the automatic wire repair are so remarkably difficult that they have been conducted exclusively off-line. Once the drawn wire has been taken up, more specifically, its flaw is either subjected, at a finishing step, to detection by the use of a nondestructive or destructive flaw detector or visually detected by human eyes if it is located in the surface. Then, the flawed portion is manually repaired by means of a grinder or the like. Despite of this fact, the off-line method of the prior art is so inefficient and uneconomical that it is tremendously troublesome, that spaces for the facilities are additionally required, and that the transporting works are complicated.
Upon elimination of the aforementioned surface flaw, on the other hand, it is being recently developed that the flawed surface portion is cut only a predetermined length all over the circumference, in view of the fact that the yield is reduced by the general example of the prior art because the wire is either peeled off its whole length over the whole circumference by means of a die or cut by means of a cutting tool on the same principle as that of a lathe. Despite this development, reduction in the yield cannot be avoided because the wire is cut all over the circumference even partially of the longitudinal direction.
We, the Inventors, have succeeded in completing the present invention by earnestly repeating the experiments and researches while amining at, as has been described hereinbefore: a first target that the batch-type treating process should be replaced by the continuous drawing process because it has a problem in efficiency and so on; a second target that the dry type process is desired from the standpoint that the wet type process cannot provide satisfactory working curcumstances but raises the cost for the facilities so that it is not acceptable; and a third target that the steps from the flaw detection to the repair are made in-line.